The present invention relates to a delay difference adjustment circuit and a phase adjuster, more particularly, to a delay difference adjustment circuit which adjusts the delay difference between delays of two signal lines (hereinafter referred to as "the delay difference") through which the two signals are transmitted, and to a phase adjuster which adjusts the phase difference between the two signals.
When the phase difference between the two clock signals flowing in a circuit is measured, each of the clock signals has been measured by a measuring instrument such as an oscilloscope by inputting them via two cables. Since the delay difference always exists even if the lengths of the two cables are equal, it is necessary to adjust the delay difference.
Referring to FIG. 5, the conventional device which adjusts the delay difference includes an observed circuit 41 which has clock signals CLK41 and CLK42 as the objects of observation, the measuring instrument 42, a variable delay circuit 43 which is located inside the measuring instrument 42 and delaying the clock signal inputted from the input IN42 by the delay amount, cables 45a and 45b. Each of the cables 45a and 45b connects the observed circuit 41 and the measuring instrument 42. When an observer supplies the clocks CLK41 and CLK42 to the measuring instrument 42 via the two cables 45a and 45b and measures these phase differences by the measuring instrument 42, firstly, the clock signals CLK41 and CLK42 are inputted to an input IN41 and IN42 of the measuring instrument 42, respectively. At that time, the display circuit 44 of the measuring instrument 42 indicates an apparent phase difference as the waveform or a phase difference, and the apparent phase is stored. Next, the observer exchanges the cables 45a and 45b. The clock signal CLK41 is inputted to the input IN42 through the cable 45b and the clock signal CLK42 is inputted to the input IN41 through the cable 45b. The next apparent phase difference is displayed in the display circuit 44 and is compared with the apparent phase difference which has been previously stored. The observer adjusts the delay amount of a variable delay circuit 43, by supplying a direction for delay amount setting to the input IN43 from the outside of the measuring instrument 42.
The conventional device, as described above, which adjusts the delay difference has had the problem that all of the operations had to be made manually to adjust the delay difference between the two clock signals which are observed via the two cables. More specifically, the observer has to perform all of a series of operations, including storing the phase differences of the two clock signals, exchanging the two cables, comparing the phase differences, and adjusting the delay amounts. Therefore, it takes inordinately amount of labor and time to adjust the delay difference.
Furthermore, since the above-mentioned conventional device is not capable of automatically adjusting the delay difference between the two cables, the phase adjustment of the clocks could not be made automatically.